1. Field of the Invention
The present invention generally relates to cardiac pacing systems and, in particular, to methods and medical devices for detecting an ischemic episode and to determine a location of ischemia in a heart of a patient.
2. Description of the Prior Art
Due to the in general poorer medical status of pacemaker and ICD patients they are subjected to an increased risk of ischemic heart disease (IHD) and myocardial infarction (MI). Ischemic heart disease can be divided into unstable and stable ischemia. Unstable ischemia is a highly life-threatening situation most often caused by an infarction of one or several coronary arteries. Sudden cardiac death depends in 90% of all cases on IHD. The possibility to survive depends on how fast the patient gets relevant treatment. Stable ischemia is very common among elderly people and the mortality is low or moderate. There is both silent ischemia and ischemia with heart pain, i.e. angina pectoris. The most common reason is arteriosclerosis in the coronary vessels. It can be treated with drugs or operatively using bypass techniques, stents, etc. When IHD progresses it may lead to myocardial infarction (MI), congestive heart failure (CHF) and/or the patients death. In fact early detection of IHD can serve as an early marker for CHF risk factor. An early detection of ischemic heart disease is thus required since that will give opportunities to prevent life threatening complications.
In light of this, a number of approaches have been made to detect ischemia with implantable medical devices such as pacing devices using the impedance of tissue. For example, in US 2006/0241357, a method and device for detecting the occurrence of ischemia using measurements of end-systolic impedances. However, a determination of a more specific location of the detected ischemia is not described US 2006/0241357.
Furthermore, in WO 93/18821 a monitoring system for monitoring the condition of a patient's body tissue, for example, to detect ischemia. The impedance of tissue between electrodes is measured for a number of different frequencies and an impedance signature is created. Ischemia causes a shift in this signature and thus the onset of ischemia can be detected by evaluating changes in the impedance signature. A more specific detection of the location of the ischemia is not described in WO 93/18821.
Furthermore, EP 1 690 566 corresponding to US 2006/0241357, U.S. Pat. No. 6,604,000 and U.S. Pat. No. 6,256,538 also present implantable medical devices incorporating an ischemia detector responsive to measured intracardiac impedance.
Thus, it remains a need within the art of a method and medical device that are capable of detecting the occurrence an ischemic episode and of determining a location of the ischemia.